gfs2: Fix invalid metadata access in punch_hole

In punch_hole(), when the offset lies in the final block for a given
height, there is no hole to punch, but the maximum size check fails to
detect that.  Consequently, punch_hole() will try to punch a hole beyond
the end of the metadata and fail.  Fix the maximum size check.
Signed-off-by: Andrew Price <anprice@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/bmap.c

@@ -1718,7 +1718,8 @@ static int punch_hole(struct gfs2_inode *ip, u64 offset, u64 length)
 	struct buffer_head *dibh, *bh;
 	struct gfs2_holder rd_gh;
 	unsigned int bsize_shift = sdp->sd_sb.sb_bsize_shift;
-	u64 lblock = (offset + (1 << bsize_shift) - 1) >> bsize_shift;
+	unsigned int bsize = 1 << bsize_shift;
+	u64 lblock = (offset + bsize - 1) >> bsize_shift;
 	__u16 start_list[GFS2_MAX_META_HEIGHT];
 	__u16 __end_list[GFS2_MAX_META_HEIGHT], *end_list = NULL;
 	unsigned int start_aligned, end_aligned;
@@ -1729,7 +1730,7 @@ static int punch_hole(struct gfs2_inode *ip, u64 offset, u64 length)
 	u64 prev_bnr = 0;
 	__be64 *start, *end;
 
-	if (offset >= maxsize) {
+	if (offset + bsize - 1 >= maxsize) {
 		/*
 		 * The starting point lies beyond the allocated metadata;
 		 * there are no blocks to deallocate.